In order to clean a solid surface so that such surface can again be coated such as, for example, to preserve metal against deterioration, or simply to degrease or remove dirt from a solid surface, it has become common practice to use an abrasive blasting technique wherein abrasive particles are propelled by a high pressure fluid against the solid surface in order to dislodge previously applied coatings, scale, dirt, grease or other contaminants. Various abrasive blasting techniques have been utilized to remove coatings, dirt, grease and the like from solid surfaces. Thus, blasting techniques comprising dry blasting which involves directing the abrasive particles to a surface by means of pressurized air typically ranging from 30 to 150 psi, wet blasting in which the abrasive blast media is directed to the surface by a highly pressurized stream of water typically 1,000 psi and above, or blasting in which both air and water are utilized either in combination at high pressures to propel the abrasive blast media to the surface, or in combination with relatively low pressure water used as a dust control agent or to control substrate damage have been used. Water for dust control has been mixed with the air either internally in the blast nozzle or external of the nozzle at the targeted surface to be cleaned and such latter process, although primarily a dry blasting technique, is considered wet blasting inasmuch as media recovery and clean-up is substantially different from that utilized in a purely dry blasting operation.
The use of blast chambers to strip contaminants from the surfaces of articles, in particular, articles which are of relatively small size is an important technique of cleaning such articles especially if blast cleaning is done on a regular basis. For example, automobile manufacturers use blast chambers to clean auto parts such as door panels, hoods, trunk tops, bumpers, etc. which have been over or unevenly painted for repainting. Blast chambers or cabinets are useful in cleaning salvaged parts and systems before they can be disassembled, inspected and rebuilt. Auto parts rebuilders, heavy machinery reconditioners, machine tool manufacturers, the airline, railroad and trucking industries, commercial vehicle leasing and military bases and depots are all examples of users or facilities where parts cleaning is done on a regular basis and can find the use of a blast chamber or cabinet beneficial.
If blast cleaning is done on a regular basis, it is important to control noise levels, capture, examine and, if possible, recycle used abrasive media and, importantly, control the dust which is formed so as to provide for the visibility of the blast nozzle operator. Dust control in blast chambers is extremely important in view of the enclosed environment which is used for the cleaning process. In the more enclosed environment of a blast chamber, the use of a secondary water stream does not effectively control the dust and, may in fact, add to visibility problems by forming a mist which stagnates in the chamber. Thus, it is often desired to blast clean using a purely dry blast cleaning process. Unfortunately, in a dry blast cleaning process, a considerably large amount of dust engulfs the environment of the target substrate.
Blast cabinets typically include an interior chamber in which the article or articles to be cleaned or treated by an abrasive media are placed. The operator usually reaches through armholes protected by rubber gloves and, observing through a front window in the blast cabinet, either picks up an article to be cleaned and moves it under a stationary blast nozzle or picks up a portable blast nozzle and moves it about to direct a high velocity stream of the abrasive particles over the surfaces of the article. The blast media typically used with a blast cabinet is a relatively hard particulate material such as steel shot, glass beads, aluminum oxide and like materials which normally experience a limited breakdown during use and is recycled for use after removing the contaminants from the treated surface.
An alternative to the hard abrasives used as a blast media, particularly, for removing adherent coatings or other contaminants from relatively soft substrates such as softer metals as aluminum, composite surfaces, plastics, ceramic tile, and the like is sodium bicarbonate. While sodium bicarbonate is relatively soft, it is sufficiently hard to remove coatings from steel and aluminum surfaces and as well remove other coatings including paint, dirt, and grease from non-metallic surfaces without harming the substrate surface. Sodium bicarbonate is not harmful to the environment and is most advantageously water soluble such that the particles which remain subsequent to blasting can be simply washed away without yielding environmental harm.
Accordingly, fine powder abrasive materials, such as sodium bicarbonate-based materials, are preferred for some applications because they are less harsh to the surface being cleaned, are nonhazardous to persons operating or working in the vicinity of blast operation including blast cabinets and the disposal of the spent media is greatly simplified. However, dry forms of this type of material generally cannot be used in a blast media in conventional bast cabinets because the material is friable and breaks down into dust-like particles which are dispersed throughout the blast cabinet and-produce a dense, fog-like condition. This condition cannot be eliminated or adequately reduced by conventional blast cabinet ventilation technology. Consequently, the operator most often is unable to observe the article being cleaned. This is particularly true for operations using higher velocity jet streams. The addition of a liquid such as water to control dust, often as before-said does not usually solve the problem as the water tends to disperse in a manner to further obscure visibility in the area surrounding the article being cleaned.
U.S. Pat. No. 5,177,911, issued Jan. 12, 1993, to Ruemelin discloses a blast cabinet with an improved ventilation system to provide better visibility of the object being cleaned with a friable abrasive such as sodium bicarbonate. In a preferred embodiment of the invention disclosed therein, there is provided an abrasive blast cabinet including a housing defining a blast chamber, a blast nozzle in the blast chamber and connected to a source of an abrasive blast media for directing a flow of the blast media carried in a pressurized stream of gas against the surface of an article to be cleaned, window means for observing the article during cleaning including an elongated tubular member having an inner end portion located inside the blast chamber and having an inner viewing port situated so that there is a viewing zone between the inner viewing port and the article being cleaned. The tubular member also has an outer end portion including an outer viewing port through which an operator located outside the blast chamber can direct his or her line of sight through the interior of the tubular member and observe the article being cleaned. Gas delivery means directs a flow of gas into the viewing zone to purge away a sufficient amount of the blast media from the viewing zone to facilitate observation of at least that portion of the article being cleaned.
While in theory, the Ruemelin cabinet disclosed in U.S. Pat. No. 5,117,911 is an improvement over previous blast cabinets in the ability thereof to improve visibility of the blast cleaning operation, in practicality, any attempt to commercialize the blast cabinet disclosed in the Ruemelin patent does not readily achieve its proposed objectives. For one, the viewing zone is very limited when utilizing the tubular viewing port. Thus, except for telescoping means to shorten or elongate the viewing chamber, the operator is very limited as to where the article to be blasted must be placed. For larger objects, this limited viewing zone could be very disadvantageous as it may not be readily possible to turn and twist such an object and maintain the object in the viewing zone limited by the tubular member disclosed in the Ruemelin patent. Further, the Ruemelin patent does not readily discuss or disclose controlling the air pressure inside the cabinet so as to insure air flow across the viewing zone and secondly, to insure that dust does not escape from the internal chamber in the cabinet. Air is constantly entering the cabinet through the blast nozzle and from the ambient environment. Accordingly, if there is not present a vacuum or suction force which can be controlled accurately, this can result in either an insufficient amount of ambient air being drawn into the cabinet for direction across the viewing zone or, too much air may be drawn into the cabinet, pressurizing the cabinet and allowing the leakage of dust into the surrounding environment and causing a nuisance and health hazard to the operator. Thirdly, while the Ruemelin disclosure suggests treatment of the air- laden dust which is withdrawn from the cabinet such as by means of bag filters, in the present environmental climate, it is virtually impossible to remove a sufficient amount of dust from the circulating air by bag filters so as to allow the filtered air to be directed into the atmosphere. There still remains in the filtered air a considerable amount of dust which is unacceptable by present environmental laws and regulations.
Accordingly, a primary object of the present invention is to provide an improved apparatus for cleaning or finishing surfaces of articles located inside a chamber with a pressurized flow of a cleaning media including an observation arrangement which facilitates observation of the portion of the article being treated in spite of the cleaning media dust which is dispersed throughout the interior of the chamber.
Another object of the invention is to provide an improved abrasive blast cabinet which is capable of employing a dry, friable abrasive material as the blast media and at the same time provide the operator with a clear view of the article being cleaned.
Still another object of the invention is provide an abrasive blast cabinet including improved viewing means for observing the article being cleaned and which can be easily adjusted to allow the operator to move the article to be cleaned within the blast chamber and still maintain a line of sight on the portion of the article being cleaned.
Another object of the invention is to provide an improved blast cabinet which contains means to accurately control the air pressure within the interior chamber of the cabinet so as to insure the flow of gas into the viewing zone of the chamber to purge away dust dispersed within the viewing zone and also prevent the leakage of dust from the chamber into the external environment of the blast cabinet.
Still yet another object of the present invention is to treat the dust-laden air removed from the interior chamber of the blast cabinet so as to remove the dust and recycle the air into the interior chamber of the blast cabinet to purge dust from the viewing zone and to provide sufficient treatment to the dust-laden air so that a portion of the treated air can be directed into the environment and comply with clean air standards.
Other objects, aspects and advantages of the invention will become apparent to those skilled in the art upon reviewing the following detailed descriptions, the drawings and the appended claims.